I have voted $4500, as that would be nice, but we are basically all armchair Product Managers on this, and I bet there is a lot to take into account that we just don’t know about.
All the previous Mac Pros have had an entry-level price that started where the iMac left off (so about $2500 in 2006, $3400 today*) - they've always come in a lovely, custom case and offered a few flourishes that you wouldn't see in a generic Xeon workstation and they've
always been BTO upgradeable to pro media monsters with 5-figure prices. Yea, even the hated trashcan met that description if you believed that external expansion and compulsory dual GPUs were the future.
At some stage in the last two years, Apple decided that it was OK to massively hike that up to $6000 - and the new Mac Pro has been designed with that in mind (seriously, if Apple
don't have at least a rough target price-point in mind when they start a design then I've got a bridge in Brooklyn that you might like to buy - to do otherwise isn't even praiseworthy, it would be incompetent and a recipe for producing an Edsel/Homer).
So that's the answer to the thread's question -
a Mac Pro should have started at around $3500, same as it always did (+ inflation). Whether or not the newly announced Mac Pro could be economically sold at that price, or easily trimmed down to meet it, is Apple's problem. Likewise, even if that infamous display stand actually costs $1000 to make and Apple are losing a dollar on every one they sell
it is still a stupid price for a display stand.
The alternative answer is that a headless Mac Pro with an 8-core Xeon W, 32GB RAM, 256GB SSD, Radeon Pro 580X and some PCI slots shouldn't cost
more than an iMac Pro with a comparable processor (basically the 2017 version of the same point in the range), the same RAM, a
better GPU, 4x as much storage and a display the equivalent of which would cost you $1300, but without the PCIe slots. Yes, folks, cramming that all into an iMac chassis and keeping it cool took some R&D too - and this armchair product manager reckons that would be a tad harder than designing a full-size PCIe motherboard for a huge tower enclosure with tons of space.
* Currently $3399 for an 8-core i9, 32GB of RAM at Apple's ridiculous BTO price, the same Radeon Pro 580X as in the new Pro and 512GB of SSD - twice what you get in the Mac Pro. OK, the pro is Xeon/ECC - but that's always been the case and past Mac Pros have still started at $2500-$3000, just as its often been the case that the top-end iMac has comparable benchmarks to the entry Mac Pro - everybody but the true haters understand why that is.